Characterization of activity and expression of isocitrate lyase in Mycobacterium avium and Mycobacterium tuberculosis

Analysis by two dimensional gel electrophoresis revealed that Mycobacterium avinm expresses several proteins unique to an intracellular infection. One abundant protein with an apparent molecular mass of 50 kDa was isolated, a nd the N-terminal sequence was determined. It matches a sequence in the M. tuberculosis database (Sanger) with similarity to the enzyme isocitrate lya se of both Corynebacterium glutamicum and Rhodococcus fascians. Only margin al similarity was observed between this open reading frame (ORF) (termed ic l) and a second distinct ORF (named aceA) which exhibits a low similarity t o other isocitrate lyases. Both ORFs can be found as distinct genes in the various mycobacterial databases recently published. Isocitrate lyase is a k ey enzyme in the glyoxylate cycle and is essential as an anapleurotic enzym e for growth on acetate and certain fatty acids as carbon source. In this s tudy we express and purify Id, as well as AceA proteins, and show that both exhibit isocitrate lyase activity. Various known inhibitors for isocitrate lyase were effective. Furthermore, we present evidence that in both M. avi um and M. tuberculosis the production and activity of the isocitrate lyase is enhanced under minimal growth conditions when supplemented with acetate or palmitate.